This invention relates to improvement in an image formation apparatus, such as an electrophotographic printer or copier, particularly including a plurality of image formation units disposed along a transfer material transport passage for successively transferring toner images to a transfer material moving on the transfer material transport passage.
Known as a conventional image formation apparatus is an apparatus called tandem type including a plurality of image formation units disposed on a transfer material transport passage extending in a horizontal direction, for example, for successively transferring toner images from the image formation units to a transfer material moving along the transfer material transport passage and forming a color image on the transfer material.
The image formation unit refers to a pair of a photoconductor unit having a photoconductor on which an electrostatic latent image is formed and a developing unit for storing toner supplied to the photoconductor. Already proposed as the transport technique is a transfer roll transport technique wherein each image formation unit is provided with a transfer roll for abutting the photoconductor and paper as a transfer material is transported by the photoconductor and the transfer roll, or a belt transport technique wherein paper is, for example, electrostatically attracted and held on a circulating transport belt.
As for the arrangement structure of the image formation units, already proposed are a landscape orientation type wherein a plurality of image formation units are placed transversely side by side relative to a transfer material transport passage extending in the horizontal direction and a portrait orientation type wherein a plurality of image formation units are placed longitudinally relative to a transfer material transport passage extending in a vertical direction.
However, in this kind of the conventional landscape orientation type, often the image formation units are attached and detached from the direction parallel with the transport face of the transfer material transport member and vertical to the transport direction. In this case, the image formation units are positioned in the apparatus main unit by an image formation unit drive member attached to one side of the apparatus main unit and a positioning member formed on an opposite side of the apparatus main unit with the transport member between.
The image formation unit itself is positioned by a positioning section formed in a support member for supporting the photoconductor without directly positioning the photoconductor as the positioning reference on the configuration. Thus, it is difficult to ensure the positioning accuracy of each image formation unit in the apparatus main unit.
As for the conventional image formation apparatus of the portrait orientation type, each image formation unit can be attached and detached from the direction orthogonal to the transfer material transport passage of roughly vertical portion, so that each image formation unit can be positioned in the apparatus main unit by a unit positioning section formed on both sides of a cabinet and it becomes easy to ensure the positioning accuracy; in contrast, however, a disadvantage occurs in the transfer material transportability.
In the transfer roll transport technique, it the image formation unit spacing is wide to some extent, paper passes through the transfer part of one image formation unit, the pass-through paper portion becomes long, the tip state of the paper becomes easily unstable in such a manner that the tip of the paper curls or remains straight, and the tip position of the paper arriving at the transfer part of the next image formation unit easily varies.
Thus, the write start position of each color component toner image relative to the paper at the transfer part of each image formation unit shifts, causing a color shift or color unevenness phenomenon of a color image.
In the belt transport technique, paper is transported on the paper transport belt and thus the tip entry position of paper in the transfer part of each image formation unit is stable and the color unevenness of a color image relative to the paper transport direction can be suppressed as compared with the transfer roll transport technique. However, as the image formation unit spacing is wider, a walk phenomenon in which when the paper transport belt moves, it meanders in the width direction increases, and color shift or color unevenness of color image worsens in the orthogonal direction (width direction) to the paper transport direction.
It is therefore a first object of the invention to provide an image formation apparatus for enabling components to be well positioned in an apparatus main unit.
It is a second object of the invention to provide an image formation apparatus for making it possible to suppress a color shift and color unevenness of a color image accompanying transport unevenness of a transfer material and miniaturize the apparatus itself.
Although the solution means of the invention will be described to the specific contents to understand the invention, it is to be understood that the claims are not substantially reduced.
To accomplish the first object, the image formation apparatus of the invention includes the developing unit placed in the apparatus main unit displaceably or in a pressed state, the photoconductor unit placed in the apparatus main unit and is positioned, and the developing unit positioned relative to the positioned photoconductor unit.
To accomplish the second object, the image formation apparatus of the invention includes at least apart of the second photoconductor unit involving the second color positioned so as to overlap the first developing unit involving the first color, placed in the apparatus main unit in the move direction at the placing time.
A supplementary description to the invention to accomplish the second object is given below:
The inventor found out that it is important to miniaturize the apparatus to suppress a color shift and color unevenness of a color image accompanying transport unevenness of a transfer material and obtained the invention.
The process to obtain the invention will be discussed specifically.
Generally, as the color shift, color unevenness amount of color image not perceived as a problem by the user of an image formation apparatus, it is said that the maximum shift amount is 150 xcexcm in the paper transport direction and is 100 xcexcm in the orthogonal direction (width direction) to the paper transport direction.
By experiment concerning this point, we found out that the transfer part spacing of each image formation unit needs to be set to 30 mm or less to place within the above-mentioned shift amount.
By the way, in the conventional portrait orientation type, generally the limit of the spacing is 45 mm.
FIG. 15 is a schematic drawing of a conventional color image formation apparatus of the portrait orientation type. It is seen that the occupation space and attachment/detachment space of each image formation unit (205a to 205d) govern the image formation unit (205a to 205d) spacing.
As the configuration of the image formation unit (205a to 205d), the color image formation apparatus is placed in the normal orientation from the viewpoint of ensuring the space of a paper transport passage in the vertical direction and when FIG. 15 is viewed from the front of the plane of the Figure to the depth, a cleaning member 273a, a charging member 236a, and light exposure means 253a as image formation means are placed in the first quadrant with respect to a photoconductor 234a, a developing member is placed in the fourth quadrant, and space of the second and third quadrants is provided as much as possible.
Assuming that the diameter of the photoconductor 234a is a, that the height of a developing unit is b, and that the occupation height of the cleaning, charging member is c, the height of the image formation unit becomes about a+(b/2)+c.
If a=16 mm, b=20 mm, and c=10 mm as the minimum possible values of a, b, and c at present, the height of the image formation unit 205a becomes 36 mm. Allowing for a gap of 2 mm as an attachment/detachment margin of the adjacent image formation unit, it is considered that the limit of the transfer part spacing of each image formation unit (205a to 205d) is 38 mm.
That is, we found out that so long as the configuration of a simple extension of related arts continues to be adopted as mentioned above, if the components are miniaturized as much as possible, shortening the transfer part spacing involves a limit and the limit does not reach the level allowed by the user.
Thus, the inventor recognized the necessity for conceiving an epoch-making configuration and thought of the invention.
This means that we set the specific numeric target of 30 mm and examined the invention to shorten the image formation unit spacing from the viewpoints of miniaturization of the whole apparatus or ensuring the run stability of a transfer material transported in the vertical direction and the run stability of a transfer material transport belt.
That is, in a first aspect of the invention, as shown in FIG. 1, an image formation apparatus includes a photoconductor unit 8 (8a to 8d) having a photoconductor 34 on which an electrostatic latent image is formed and a developing unit 6 for storing toner supplied to the photoconductor, wherein the developing unit 6 is displaceably placed in an apparatus main unit and then the photoconductor unit 8 is detachably placed in the apparatus main unit and is positioned at a predetermined position, whereby the displaceable developing unit 6 previously placed is positioned relative to the photoconductor unit 8.
Such technical means is effective not only for a tandem image formation apparatus for forming a color image, but also for a single-color image formation apparatus on the configuration, of course.
Unit guide and positioning member and the unit shape may be selected appropriately and at least a photoconductor and a charging member may be built in the photoconductor unit and any other process means, such as a cleaning member or an electricity removal member, may be included as required, of course.
As for the developing method, an image support and various functional parts required for developing may be built in appropriately and various developing techniques may be adopted regardless of the developer type, contact developing or non-contact developing.
Developing unit guide part may be selected appropriately corresponding to the structure of the developing unit if the developing unit can be displaceably positioned in the same attitude for the corresponding guide part.
For example, if the developing unit guide part is provided with one displacement concave part, the developing unit may be provided with a positioning convex part fitted in a positioning-possible manner corresponding to the displacement concave part.
The unit positioning member of the photoconductor unit may be selected appropriately corresponding to the structure of the unit positioning member if it positions the photoconductor unit relative to the corresponding unit positioning part.
For example, if the unit positioning member is provided with a positioning concave part or a positioning pin, the photoconductor unit may be provided with a positioning convex part or a positioning groove fitted in a positioning-possible manner corresponding to the positioning concave part or the positioning pin.
To maintain good quality of an image developed on the photoconductor, the developing unit may be urged to the photoconductor unit side by a press member of a spring, etc., disposed in the apparatus main unit and a part of the developing unit may be abutted against the photoconductor of the photoconductor unit, whereby the developing unit may be positioned relative to the photoconductor unit.
Further, the guide and positioning member of the photoconductor unit and the developing unit is configured integrally, it is advantageous from the viewpoint of ensuring the attachment accuracy of the photoconductor and the developing roll. Particularly, preferably such a positioning structure minimizing an eccentric error of the photoconductor is adopted from the viewpoint of holding color registration good. It is desirable that the guide and positioning member of each unit should be attached to the apparatus main unit as an integrally configured member so that the pitch between the image transfer positions of each photoconductor unit becomes equal with high accuracy.
Further, the developing unit is displaceably placed at a predetermined position through a placement opening of the apparatus main unit and then the photoconductor unit is detachably placed in the apparatus main unit through the placement opening and at least a part of the photoconductor unit is positioned at a position overlapping the developing unit on the side near to the placement opening from the predetermined position and in the move direction to the placement opening, so that the height direction dimension of the image formation unit may be shortened as much as possible.
Further, another adjacent photoconductor unit is detachably placed in the apparatus main unit through the placement opening and at least a part of the photoconductor unit is positioned at a position over lapping the first developing unit on the side near to the placement opening from the predetermined position and in the move direction to the placement opening, whereby the image formation unit spacing can be more shortened.
When the image formation units are placed longitudinally, to take out the photoconductor unit and the developing unit of the same color, the adjacent photoconductor unit for a different color must first be taken out because of the positional relationship between the developing unit and the adjacent photoconductor unit for the different color overlapping each other.
However, in the recent tandem color image formation apparatus, as the developing technique of a developing unit, a dual-component developing technique is mainstream and it is expected that the developing unit itself will have a prolonged life. In this case, as the developing unit, importance is attached to the purpose of avoiding the risk of dropping the developing unit, mixing a foreign substance in the developing unit, etc., as the user removes the developing unit willfully.
Therefore, in such a form, a fixing member may be disposed so that the developing unit cannot easily attached to or detached from the apparatus main unit, and only the photoconductor unit may be able to be attached to and detached from the apparatus main unit.
Further, the transport and transfer member may be of any type if it transfers a toner image to a transfer material while giving a transport force to the transfer material; preferably a transfer roll a transfer roll to which a transfer electric field is applied is used from the viewpoint of a simple and small-sized device.
Further, if a transfer material is transported by the transport and transfer member, nothing may be provided before each image formation unit. However, preferably a transfer material guide for guiding a transfer material into the nip part between the photoconductor and the transport and transfer member is provided before each photoconductor unit from the viewpoint of more stably transporting the transfer material. However, the transfer material transport member and the transfer material guide need to become similar positional relationship to the corresponding photoconductor.
In such an aspect, the roughly vertical direction portion of a transfer material transport passage may have a plurality of transfer members and transfer material guides having the transfer material transport capability at the positions corresponding to the photoconductors of the photoconductor units, the plurality of transfer members may be positioned relative to the corresponding photoconductors through transfer member reception parts formed on both sides of the apparatus main unit, and the roughly vertical direction portion of the transfer material transport passage having the transfer member may be supported so that it can be opened and closed relative to the apparatus main unit.
In a second aspect of the invention, as shown in FIG. 9, if narrow pitch longitudinal placement of a plurality of image formation units is made possible, the maintenance space of each photoconductor unit becomes narrow and replacement becomes hard to perform.
In this case, an image formation apparatus comprises a plurality of developing units for storing different color toners to form a color image and a photoconductor unit group 50 for supporting on a single cabinet a plurality of photoconductors on which electrostatic latent images are formed, the electrostatic latent images being developed by the developing units, characterized in that the developing units are displaceably placed in an apparatus main unit and then the photoconductor unit group is detachably placed in the apparatus main unit and is positioned at a predetermined position, whereby the displaceable developing units previously placed are positioned relative to the photoconductors of the photoconductor unit group.
In such technical means, the unit guide and positioning member and the unit shape may be selected appropriately and at least as many photoconductors and a charging member as capable of forming a color image may be built in the photoconductor unit group and any other process means, such as a cleaning member or an electricity removal member, maybe contained as required, of course.
As for the developing method, various developing techniques may be adopted as described in the first aspect of the invention.
Further, the unit shape, the shape of the unit guide and positioning member, the developing unit positioning method relative to the photoconductors of the photoconductor unit group, and the like are similar to those previously described in the first aspect of the invention.
Next, the function and effect of the technical means as described above will be discussed. To begin with, in the configuration shown in FIG. 1, the integral-type image formation unit in the related art is divided into the photoconductor unit and the developing unit, so that the layout of the units is made flexible and it is made possible to place the image formation units with narrow pitches as compared with the integral-type image formation unit.
Further, the assembling accuracy of the photoconductor unit and the developing unit, which becomes disadvantageous as the integral-type image formation unit is divided, can be ensured by a single member of a pair of unit guide and positioning members of integral type attached to both sides of the apparatus main unit.
Further, the image formation apparatus has the advantage that the rotation center shaft of the photoconductor of the photoconductor unit can be directly positioned and supported.
It is also made possible to position the developing unit relative to the photoconductor.
Further, in the configuration shown in FIG. 9, a plurality of photoconductor units are put into one piece, whereby the positioning parts in the apparatus main unit can be reduced to a single part, so that parts management of the apparatus main unit is facilitated and it is made possible to improve the accuracy and simplify the apparatus configuration.
In a third aspect of the invention, as shown in FIG. 10, an optical unit includes an incidence optical member for giving a different angle to each of a plurality of laser beams to form a color image and making the laser beam incident on a single polygon mirror rotation body (which will be herein after referred to as polygon mirror) rotating at high speed, a single image-forming lens having Fxcex8 characteristic through which the laser beam for each color reflected on the polygon mirror passes through, a first reflecting mirror for reflecting the laser beam for each color after passing through the image-forming lens in the opposite direction to the incidence direction, and a plurality of second reflecting mirrors for forming an image of each reflected laser beam reflected on the first reflecting mirror on an image formation position for each color, so that the color laser beam spacing can be adjusted as desired in the optical unit (for example, by changing the installation angle of the second reflecting mirror or the like) and thus the image formation unit spacing, can be shortened independently of placement of the optical unit. In such technical means, as the image formation unit, preferably the peripheral parts of an image support are put into a cartridge as much as possible considering the mount workability, etc., and use of a drum-like photoconductor as the image support is suited for short spacing.
Further, a transport and transfer member is any if it transfers a toner image to a transfer material while giving a transport force to the transfer material. Preferably, a transfer roll to which a transfer electric field is applied is used from the viewpoint of a simple and small-sized device. Further, if a transfer material is transported by the transport and transfer member, nothing may be provided before each image formation unit. However, preferably a transfer material guide for guiding a transfer material into the nip part between the image support of each image formation unit and the transport and transfer member is provided before each image formation unit from the viewpoint of more stably transporting the transfer material.
Ball bearings or plain bearings of resin material resistant to temperature change and abrasion support the outer peripheral surface of the image support for rotation, thereby suppressing run-out of each image support and a single endless belt is pressed against the outer peripheral surface of each image support and is frictionally driven, thereby setting the image supports to the same peripheral speed. Assuming that the transport speed of nip transport member of a pair of a registration roll and a pinch roll on the entrance side of the upstream image formation unit is V1, that the transport speed of fuser nip transport member on the exit side of the downstream image formation unit is V3, and that the peripheral speed of each image support is V2, the relation V1xe2x89xa7V2xe2x89xa7V3 is provided, whereby slack in a transfer material is produced on the nip upstream side of the upstream image support and transfer roll and on the fuser nip transport upstream side on the exit side of the downstream image support and transfer roll, and the effect of transport speed unevenness caused by nip transport on the entrance side and the exit side to the transfer material in the transfer part of the transfer roll and the image support can be ignored; it can be expected that a color shift and color unevenness of a color image accompanying transport unevenness of the transfer material can be suppressed.
The arrangement order of the image formation units may be set appropriately. Preferably, the downstream image formation unit forms a black toner image from the viewpoint of maintaining good image quality in a single-color black mode frequently used. The configuration in FIG. 13 is almost similar to that of the color image formation apparatus of the third aspect and therefore will not be discussed again. A transfer belt is selected as transfer material hold transport member. In the form, the apparatus itself is also upsized, the number of parts is also increased, and the cost is also increased as compared with the transfer roll transport member described above. However, as the transfer member, it is not indispensable to particularly give a transport force to a transfer material and thus the transfer member is not limited to transport and transfer member such as the transfer roll and may be a part such as a metal transfer roll of stainless steel, etc. Since it is not necessary to forcibly set the image supports to the same peripheral speed and the image formation unit spacing can shortened, it is made possible to reduce the peripheral length of the transport belt to a half or less as compared with that in the related art, a walk phenomenon in which when the paper transport belt moves, it meanders in the width direction can be suppressed, and color shift and color unevenness of the color image is improved in the orthogonal direction (width direction) to the paper transport direction.
In a fourth aspect of the invention, as shown in FIG. 14, an optical unit includes an incidence optical member for giving a different angle to each of a plurality of laser beams to form a color image and making the laser beam incident on a single polygon mirror, a single first reflecting mirror for reflecting the laser beam for each color reflected on the polygon mirror in the opposite direction to the incidence direction, and a single or a plurality of second reflecting mirrors having reflection and Fxcex8 characteristics for forming an image of each reflected laser beam reflected on the first reflecting mirror on an image formation position for each color. Thus, similar advantages to those in the third aspect can be provided.
In a fifth aspect of the invention, as shown in FIGS. 10, 13, and 14, the reflection direction angle difference between the reflected laser beams each for each color reflected on the second reflecting mirror of the optical unit is set within 10 degrees, whereby the developing device configurations of the image formation units are made the same, it becomes easy to combine the developing characteristics of the image formation units, and the reliability of the image quality is also enhanced.